Answer

Unreal Engine, developed by Epic Games, is not open source; it is a proprietary game engine available under a source-available license. This means that while the source code of the engine can be accessed and modified by developers, there are restrictions placed on its use according to a licensing agreement.

Here’s what you need to understand about Unreal Engine’s accessibility:

1. Source Code Access: Developers registered with Epic Games have access to the Unreal Engine source code via GitHub. This allows them to study and modify the engine for their needs but does not grant the same freedoms as an open-source license, such as those defined by the Open Source Initiative (OSI).

2. Licensing Terms: Even though modifications are allowed, the terms require any commercial products made with Unreal Engine to pay royalties after a certain revenue threshold is reached.

3. Contributions: Developers can contribute to the Unreal Engine source code. However, contributions must be approved by Epic Games, and contributors must agree to Epic’s terms, which typically involve granting Epic a license to use the contributed code.

Due to these conditions, Unreal Engine straddles between being proprietary software and offering some benefits similar to open-source projects. The availability of the source code encourages learning, customization, and a collaborative development environment, albeit under controlled circumstances.